Aggregates, i.e., crushed stone, sand and gravel, are the most fundamental components used in construction. Approximately fifty percent of aggregates are shipped for highway construction, either as a road base or a primary component of asphalt and concrete. Aggregates are also used in commercial and residential construction as a base for foundations, concrete and parking lots. Other uses for aggregates, some of which require a high-quality, chemical-grade limestone, include: riprap for erosion control; railroad ballast; flux stone; filter stone; agricultural limestone; production of cement and lime; desulfurization; acid neutralization; animal feed supplements; and plastic and paint fillers. Regardless of the use, the production requirements of stone aggregates are complex because the material must be crushed to multiple sizes, often washed to remove fines and impurities, and sometimes processed further in order to meet the specification for its intended use. Without the physical and chemical properties provided by aggregates, modem construction materials and methods, as well as a multitude of industrial products, would not be possible.
Product requirements often dictate the percentages of flat particles, elongated particles or flat and elongated particles in coarse aggregates, i.e., crushed stone or gravel that will not, when dry, pass through a sieve with specified diameter holes. For example, flat or elongated particles of aggregates for some construction uses may interfere with consolidation and result in harsh, difficult to place materials. Flat particles are defined as those particles that exceed a specified ratio of width to thickness. For example, if the ratio is 3:1, the width cannot exceed three times the thickness. (A specification will give a percentage and then the ratio, such as 20% 3:1, meaning a sample fails the specification if more than 20% of the particles (individual pieces) tested have ratios that exceed 3:1.) Elongated particles are defined as those particles that exceed a specified ratio of length to width. Flat or elongated particles are defined as those particles of aggregate having a ratio of width to thickness or length to width greater than a specified value. Flat and elongated particles of aggregate are defined to be those particles having a ratio of length to thickness greater than a specified value.
Sieve size is the size of an opening that a particle can pass through. The specification may require that the amount of particles passing through the opening be determined ("percent passing"). Or, the specification may require that the percent of the sample that does not pass through a specified opening be determined ("percent retained").
Aggregate size refers to a description of the product based on how much of the product passes (or could be given as how much is "retained on") a specified number of sieve sizes, or openings. For example, an ASTM (American Society of Testing and Materials) #57, a typical product used in concrete and asphalt construction, is described by using sieve sizes as follows (sieve sizes are square openings):
______________________________________ Sieve Size % Passing ______________________________________ 1 1/2 inches 100% 100% of the sample must pass through an 1 1/2 inch square opening 1 inch 95-100% Between 95 and 100% of the particles must be smaller than 1 inch 1/2 25-60% Between 25 and 60% of the particles must be smaller than 1/2 inch #4 0-10% #4 is close to 1/4 inch opening #8 0-5% #8 is close to 1/8 inch opening ______________________________________
Prior apparatus and methods for measuring individual particles of aggregate of specific sieve size to determine the ratio of width to thickness, length to width, or length to thickness include that disclosed in Standard Test Method for Flat Particles, Elongated Particles, or Flat and Elongated Particles in Coarse Aggregate, ASTM Designation D 4791-95, the entire contents of which are incorporated herein by reference. Referring to prior art FIG. 1, which is a schematic of a proportional caliper device 1' that consists of a base plate (not shown) with two fixed posts 3a' and 3b' and a swinging arm 4' mounted between them so that the openings (larger opening, not shown) and (smaller opening, not shown) between the swinging arm 4' and the two fixed posts 3a' and 3b' maintain a constant ratio. The axis position 6' can be adjusted to provide the desired ratio of opening dimensions. FIG. 1 illustrates a device on which ratios of 1:2, 1:3 and 1:5 may be set (6a', 6b' and 6c', respectively). The axis position 6' must be moved to change the ratio being measured. A complete re-measuring of the particle under test each time a new ratio is selected (axis position 6' is moved) is thus required. The device disclosed in FIG. 1 is capable of measuring only one ratio at a time and is therefore capable of only determining whether a particle is larger or smaller than a single ratio.
Referring to FIG. 2 and FIG. 3, FIG. 2 and FIG. 3 are schematics showing the use of the prior art device of FIG. 1 to (1) measure the elongation of aggregate particles and (2) measure the flatness of aggregate particles, respectively. A sample of aggregate particles is prepared pursuant to the methods disclosed in D 4791-95. The ratios of particle dimensions are then determined using the proportional caliper device 1' of FIG. 1. The determination of ratios of particle dimensions may be reported by mass or by particle count. If reported by mass, the sample is first dried at a temperature of about 230.degree. F. (approximately 110.degree. C.) to ensure constant mass. The sample of coarse aggregate to be tested is sieved and each size fraction larger than the 9.5-mm (3/8-in.) sieve present in the amount of 10% or more of the original sample is reduced until approximately 100 particles are obtained. The proportional caliper device 1' is then positioned at the specified ratio and the particle test is run as follows: Flat Particle Test (FIG. 3)--the larger opening 5a' equal to the particle width is set. The particle 7 is flat if the thickness can be placed in the smaller opening 5b'. Elongated Particle Test (FIG. 2)--the larger opening 5a' equal to the particle length is set. The particle 7 is elongated if the width can be placed within the smaller opening 5b'. After the particles have been classified into groups, the proportion of the sample in each group is determined by either count or by mass, as required. Flat and Elongated Particle Test--each of the particles in each size fraction is tested and placed in one of two groups: (1) flat and elongated or (2) not flat and elongated. The proportional caliper device 1' is set at the desired ratio as shown in FIG. 2. The larger opening 5a' equal to the particle length is set. The particle 7 is flat and elongated if the thickness can be placed in the smaller opening 5b'. After the particles have been classified into groups, the proportion of the sample in each group is determined by either count or mass as required. The percentage of flat and elongated particles to the nearest 1% for each sieve size greater than 9.5 mm (3/8-in.) is calculated.
Occasionally, AASHTO (American Association of State Highway Transportation Officials) changes specifications from one ratio requirement to another and many states have ratio requirements that differ from the AASHTO ratios to determine flat and elongated particle shape failures. The measurements to determine the relative proportions of a sample of particles, which are generally carried out on a sample of 100 particles or more, are conducted on one aggregate particle at a time. The ability to measure two or more ratios simultaneously would save time and effort on an already tedious procedure.
There therefore remains a need for better apparatus and methods that are capable of measuring the dimensions of particles in order to determine whether the particles meet product specifications.